Chest drainage apparatus

ABSTRACT

This invention relates to a novel and improved chest drainage apparatus characterized by a bottle housing a fluid collection chamber and a fluid inlet connectable to receive fluid and air from a chest cavity to be drained, air inlet and exhaust ports downstream of the fluid inlet open to the atmosphere within the air space above the fluid collected, and a U-tube between the fluid inlet and the air exhaust port capable of collecting and retaining an amount of fluid effective to provide a visual indication of any air flow into the system; a subassembly including an air chamber containing a check valve effective when connected to receive air from the exhaust port of the bottle to prevent the backflow thereof into the system; and a negative pressure relief valve connected to the air intake port automatically operative to limit the negative pressure, if any, in the air space above the fluid to a predetermined maximum. The invention also encompasses such an apparatus wherein the subassembly is detachable from the bottle and the latter is used by itself in inverted position as a reservoir of chest fluids that may be reintroduced back into the body. Also included in the apparatus in its preferred form are a positive pressure relief valve downstream of the check valve in the air chamber automatically operative to maintain the air pressure in the latter at or below a predetermined maximum. Additional novel features are those which permit removal of some of the collected fluid either for the purpose of analysis or to extend the capacity thereof.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 909,779,filed Sept. 19, 1986, application Ser. No. 553,992, filed Nov. 21, 1983,application Ser. No. 156,920, filed June 6, 1980 and application Ser.No. 341,877, filed Jan. 22, 1982, said application Ser. No. 341,877having been divided from application Ser. No. 156,920.

BACKGROUND OF THE INVENTION

Removing fluids and air from the chest cavity while preventing air fromre-entering is an old and well-practiced technique. Under emergencyconditions and perhaps at other times where nothing else is available,things like vaseline-coated gauze are used over an open chest wound.Under similar circumstances, one-way flaps made of rubber or plastichave been used for this same purpose along with other contrivances toonumerous to mention.

FIELD OF THE INVENTION

Somewhat, but not a great deal, more sophisticated mechanisms aregenerally used under controlled conditions such as those which exist inthe operating room while performing chest surgery. The simplest of thesemechanisms is a so-called "water seal" which is nothing more than abottle to receive the drained fluids and air that is partially filledwith sterile water, saline or the drained fluids themselves that has thechest drainage tube from the patient opening beneath the surface of thisbody of fluid so that the air cannot return by the same route. Such atrap was, and to some extent still is, used with a fluid collectionbottle serially connected to the latter but upstream thereof.

The next degree of sophistication added many years ago to the two-bottlechest drainage system described above was a third bottle, againconnected serially to the other two, but this time downstream thereof.This third bottle served the function of regulating the vacuum impressedupon the patient's pleural cavity to suck the fluids and air therefrom.It included a tube open to the atmosphere at one end and with the otherend opening a preset distance below the level of a supply of fluidcontained therein. Functionally, at such time as the negative pressurein the system reached the predetermined level established by the head offluid above the underwater inlet to the pressure-equalizing tube, itwould suck in air from the atmosphere. In this way the patient wasprotected against negative pressures being impressed upon his or herchest cavity that exceeded a present level. This three-bottle system didnot, however, measure the negative pressure to which the patient's chestcavity was subjected. It only placed an upper limit thereon. Thus, witha three-bottle system, the patient is fully protected even if thesuction pump fails in the open state or the vacuum line becomesaccidently disconnected.

The fourth and final bottle added to the three-bottle system included avent operative to relieve pressure therein at such time as it rose to apredetermined level. Excessive pressures build-up can occur if, forexample, the vacuum pump were to fail in the closed state or the tubeleading thereto becomes obstructed and the patient has an active airleak. Under such circumstances, a positive pressure can build up in thepatient's pleural cavity leading to what is known as "tensionpneumothrax" which can and often does have fatal consequences.

DESCRIPTION OF THE PRIOR ART

The prior art patented chest drainage bottles are, so far as applicantis aware, all owned by Deknatel, Inc. of Queens Village, Long Island,N.Y. Specifically, applicant is aware of their U.S. Pat. Nos. 3,363,627;3,559,647; and, 3,683,913, all of which relate to some form ofmulti-compartmented chest drainage apparatus. All three of these patentsdisclose bottles with a plurality of fluid-filled chambers therein, atleast one of which forms the traditional water seal of the prior arttwo, three and four bottle system while a second defines an underwatersafety seal that prevents the build-up of positive presence above apredetermined value.

The aforementioned Deknatel chest drainage bottles are in widespread usetoday throughout the United States and elsewhere and they perform wellto collecting fluids drained from the chest cavity while, at the sametime, protecting the latter from excessively high pressures, bothpositive and negative. These units do, however, have one seriousdrawback and that is the necessity for printing them before use. Infact, even during use they must be reprimed at intervals because ofevaporation which lowers the fluid levels therein and thus changes thepressures at which the "fail-safe" features are designed to function.

SUMMARY OF THE INVENTION

It has now been found in accordance with the teaching of the instantinvention that this and other shortcomings of the prior art chestdrainage systems can be overcome by the simple, yet unobvious, expedientof eliminating all underwater seals and pressure regulating systemspredicated upon fluid head and replacing them with suitable fluidlessvalve mechanisms that provide accurate pressure regulation, bothpositive and negative, along with foolproof reverse flow protection. Inaddition, the instant system not only provides for negative pressureregulation but, in addition, the continuous monitoring thereof. Anincidental, but nonetheless important, advantage of the system thatneeds no priming is the fact that the fluid-filled bottle can be used asa reservoir for returning the fluids collected to the patient's chestcavity, a function that the prior art chest drainage bottles cannotperform. Yet another feature of the instant system which finds nocounterpart in the prior art is a transparent fluid-filled U-tubeindicator that not only surges back and forth in response to theinhalations and exhalations of the patient but, in addition, providesthe observer with a visual indication of any air flowing in the system.Last, but by no means least, is the novel construction wherein all theprecision elements of the drainage apparatus are confined to one smalldetachable subassembly and a poppet-type pressure relief valve thusenabling the fluid collection bottle a relatively imprecise element thatcan be fabricated by high volume, low cost mass production techniqueswithout adversely affecting the overall precision of the system.

It is, therefore, the principal object of the present invention toprovide a novel and improved chest drainage apparatus.

A second objective is the provision of apparatus of the typeaforementioned which requires no priming, either initially or duringuse.

Another object of the within described apparatus is that of providing alow precision fluid collection bottle and a high precision subassemblyfor use therewith which, along, with a poppet-type pressure reliefvalve, all cooperate to produce a system possessing, for all practicalpurposes, the same high degree of precision as its most precise part.

Still another objective is the provision of a chest drainage systemwherein the fluid collection bottle that forms an integral part thereofcan be used as a reservoir for returning the fluids collected to thechest cavity by merely disconnecting and removing one detachablesubassembly therefrom and shutting off the drainage tube.

An additional object is to provide an apparatus of the type hereindisclosed and claimed for draining the chest cavity which provides avisual indication of any air flow in the system and, in addition,monitors the negative pressure.

Further objects are to provide a chest drainage apparatus which is safe,relatively inexpensive to manufacture, simpler than the prior artmulti-chambered chest drainage bottles, is convenient to use, versatile,compact, lightweight and even decorative.

Other objects will be in part apparent and in part pointed outspecifically hereinafter in connection with the description of thedrawings that follows.

FIG. 1 is a front elevation, portions of which have been broken away andshown in section, revealing the chest drainage apparatus of the presentinvention in its entirety;

FIG. 2 is a horizontal section therethrough taken along line 2--2 ofFIG. 1;

FIG. 3 is a fragmentary section to the same scale as FIG. 1 showing thehigh negative pressure relief system of the apparatus in operation;

FIG. 4 is a fragmentary vertically offset section taken along line 4--4of FIG. 1 and to the same scale as the latter; and,

FIG. 5 is an elevational view, portions of which have been broken awayand shown in section, to a slightly smaller scale than FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring next to the drawings for a detailed description of the presentinvention and, initially, to FIG. 1 for this purpose, reference numeral8 broadly designates the chest drainage apparatus in its entirety whilenumerals 10 and 12 similarly designate the bottle and the controlsubassembly, respectively. Subassembly 12 is detachably connectable tothe bottle and it includes a check valve 14, a positive pressure reliefvalve 16 and a control valve 18 that regulates the negative pressure inthe system. Another element forming a part of subassembly 12 and whichwill be described in greater detail presently is a negative pressuregauge 24 that also opens onto the interior of air chamber 20.

Bottle 10, in the particular form illustrated in FIGS. 1 and 2 will beseen to comprise a unitary blow-molded reservoir defining, among otherthings, a series of three fluid collection chambers 26A, 26B and 26Cseparated from one another by partitions 28A and 28B that each containsopenings 30A and 30B, respectively, near the top thereof that permit thechest drainage fluids to pass freely from the first to the second whenthe first is full and from the second to the third when both of thefirst two are full. These partitions 28 are shown as being double walledand also having an integrally-formed web 32 bridging the gap leftbetween the double walls. This same web extends along the bottom of thebottle and across the top except for the notched-out portion 34 intowhich subassembly 12 is inserted. Vertically-slotted clips 36 onopposite ends of subassembly 12 slide down the opposed margins 38 of web32 that border the sides of notch 34 thus detachably-mountingsubassembly 12 within the confines of the latter. When thus mounted,tubular air inlet 40 opening into the bottom of air chamber 20 throughcheck valve 14 will be axially aligned with the air outlet 42 in the topof bottle 10. A short hose connection 44 completes the air connectionbetween bottle 10 and the air chamber 20 of subassembly 12.

The bottle is molded from a transparent material that will show thelevel of the fluid in any of the fluid chambers 26. Each of these threechambers has the front face thereof covered by an adhesive-backed paperlabel 46 or other suitable scale-carrying member having a vertical slot48 therein through which the fluid level is visible. The label hasprinted upon its surface a volumetric scale 50 indicating the totalvolume of fluid stored at the liquid level visible through slot 48 inthe last of the chambers containing fluid. For instance, chamber 26A ofthe particular bottle illustrate will hold a maximum of 700 cc's offluid before overflowing into second chamber 26B. This second chamber,in like manner, will hold another 700 cc's even though it can only fillto the level of partition 28B before spilling over into the thirdchamber 26C. While chamber 26B fills to a level lower than 26A, it holdsthe same amount due to the truncated corner 52 of the latter. The thirdchamber 26C is similarly truncated and is designed to fill to the samelevel as chamber 26B and thus holds less than the other two,specifically, 600 cc's giving a total fluid storage capacity of 2000cc's. The paper label also provides the nurse with a convenient way ofrecording thereon the fluid level in the bottle at any observed time.

While on the subject of fluid storage capacity, reference should be madeto FIGS. 1, 2 and 5, and note should be taken of recess 54 in the backwall of chamber 26A which has an opening 56 at its deepest point sealedby a puncturable grommet 58. If perchance, the bottle is filled to nearfull capacity, a sterile needle (not shown) can be introduced intochamber 26A through conventional resealable grommet 48 and used towithdraw a considerable quantity of the fluid contained therein thusextending the normal maximum capacity of the bottle. Instances also areencountered occasionally where the capacity of the bottle is too largesuch as when draining fluid from the chest cavity of an infant or smallchild. Under such circumstances, it may be desirable to introduce fluidinto one or more of the chambers in the form of sterile water or saline.Grommet 58, therefore, can serve either the functions of infusion orwithdrawal of fluids from the bottle. The recessed relation of thegrommet makes it easier to keep clean and free of contaminants thatmight otherwise find their way into the bottle when the grommet isentered.

From a functional standpoint, the three serially-connected chambers 26A,B and C are the full equivalent of a single thin chamber three times asdeep because both provide precise volume control unattainable with asingle shallow chamber of the same capacity. The space-saving advantagesof the side-by-side multiple chamber configuration are obvious as arethe equally significant gains in terms of simplicity of manufacture. Itshould be emphasized, however, that these three chambers 26 are usedexclusively as reservoirs for the storage of fluid and they have noother function whatsoever; whereas, the prior art multi-compartmentbottles each have one or more compartments that must be primed withwater which changes their character from that of pure fluid storagevessels to something else. The bottle 10 of the instant chest drainageassembly, therefore, requires little in the way of precision and is thusintended to be disposed of following a single was or repeated use by thesame patient. All the precision-made parts of assembly 8 are confined tosubassembly 12 with the exception of negative pressure relief valve 60which is of the conventional poppet-type except that it contains abacterial filter.

The novel aspects of the bottle 10 are not found in the fluid collectionchambers 26, but rather, in such unique features as transparent U-tube62 formed at the entrance to the fluid collection and storage areadefined by compartments 26. The entrance 64 to this U-tube is also thesingle fluid inlet to the system and it is connected directly to thepatient's chest cavity by drainage tube 66. In the particular form shownin FIG. 1, a fluid-tight two-part combination connector and coupling ofstandard design 68 is interposed between the discharge end of thedrainage tube and the inlet 64 to the bottle.

Referring specifically, once again, to FIG. 1, it can be seen that asmall volume of fluid 70 will be trapped within the bend in U-tube 62once fluid begins flowing from the patient. While this U-tube could beprimed with a few cc's of sterile water or saline through puncturablegrommet 72 disposed near the low point thereof, priming is unnecessarybecause, in a sense, it is self-priming once fluid begins to flow fromthe chest cavity. As was the case with grommet 58, grommet 72 can alsobe used for the purpose of aspirating or otherwise withdrawing a sampleof drained fluid to be cultured.

The fluid 70 contained within U-tube 62 is not a water seal effective toprevent the return of air to the patient and, as a matter of fact, thechest drainage assembly of the present invention will perform quiteadequately whether there is any fluid in the U-tube or not andirrespective of its level. This is not to say, however, that the fluidfilled U-tube has no function. On the contrary, it performs two verysignificant ones, namely, as both an air leak detector and an indicatorof the inhalations and exhalations of the patient as it fluctuates andalternately rises higher in one leg of the U-tube than the other. As thesmall amount of fluid in the U-tube thus oscillates back and forth underthe influence of the differences in pressure caused by the patient'sbreathing pattern, it provides a clear visual indication that thepatient is, in fact, breathing.

The other important functional aspect of U-tube 62 is that of providinga leak detector effective to provide the observer with an instant visualindication of either an air leak in the system or the more seriousconsequence of an air leak originating in the patient's chest. If,perchance, air bubbles are detected bubbling in a downstream directionthrough the fluid in the U-tube, the drainage tube 66 should not beeither clamped off or removed from the patient until the source of theleak is located. Other than a system leak, the source of air enteringbottle 10 comes either from air leaking from the patient's lungs or,alternatively, from aid displaced from the chest cavity by the drainingfluid.

The sole function of the so-called water seals in the prior art chestdrainage systems is that of preventing the backflow of air into thepatient's chest cavity. Such systems must be primed before the waterseal becomes operative as previously note. In the instant chest drainagesystem, on the other hand, no such fluid seal is present because thefluid in U-tube is fully capable of passing air in either direction,i.e. back into the patient as well as out. Instead, a high precisionflapper-type check valve 16 located at the interface between fluidcollection chambers 76 and the air chamber 20 of subassembly 12 answersthis need. Valve 16 responds to an opening pressure of approximately 0.5cm H₂ O in the particular embodiment illustrated and it functionscompletely independently of any fluid present in either the fluidcollection chambers or the U-tube.

The full line position of FIG. 1 is the normal operating condition ofthe system, assuming some air is being evacuated from the patient'schest cavity. Fluids, mostly blood, enter the system through drainagetube 66 when they are collected in chambers 26 after having passedthrough the U-tube. The air, in turn, while passing through the fluid inthe U-tube, bypasses any fluid collected in the fluid collectionchambers and, instead, exits the latter through check valve 14 directlyinto air chamber 20. Under normal operating conditions, a negativepressure environment will exist in chamber 20 due to the vacuum beingdrawn therein by vacuum line 22 or, alternatively, this line may be leftopen to the atmosphere for gravity operation. Positive pressure reliefvalve 16 in the top of chamber 20 will normally remain closed. Whenmaintaining a sub-atmospheric pressure in chamber 20, the fluids and airare aspirated from the patient without he or she having to exert thepositive pressure required to force them out.

Vacuum line 22 is connected directly into a vacuum source supplied bythe institution. Since such systems provide negative pressures of amagnitude well in excess of that required for chest drainage purposes,the outlet 74 thereto leading out of air chamber 20 is provided with ascrew-type pressure regulator 18 operative to control the pressurewithin the latter and thus the opening pressure of check valve 16 withincarefully controlled rather narrow limits.

Now, in the rare event that a malfunction occurs of the type that wouldresult in a positive pressure build-up in air chamber 20, such ahappenstance having been indicated by the kinking of the vacuum line 22shown in phantom lines in FIG. 1, the remote possibility arises thatsuch a positive pressure could blow out check valve 16 thus releasingthis pressure back into the chest cavity of the patient with theattendant serious consequences. To prevent this from every happening,positive pressure relief valve 14 is provided in subassembly 12 for thepurpose of venting any positive pressure above a predetermined value tothe atmosphere before it can re-enter the system. Valve 14 like valve 16is of the flapper type and set to open at a pressure well below thatwhere valve 14 would be over-ridden and allow air back into the system.The phantom line positions of valves 14 and 16 represent the abnormalpositive pressure relief condition just described. It should, perhaps,be noted that the open positions of both these valves have been highlyexaggerated in FIG. 2 for purposes of illustration since they actuallyhave to only unseat a tiny fraction of an inch to accomplish theirintended functions.

One of the most significant and unique features of the chest drainagesystem forming the subject matter hereof is the negative pressureindicator identified by reference numeral 24 and which forms an integraland functional part of subassembly 20 and which has been shown mostclearly in FIGS. 1 and 3 to which detailed reference will now be made. Avertically-disposed upwardly-flaring frustoconical tube 76 opens intothe bottom of the air chamber 20 through restricted opening 78 therein,such opening being too small to pass ball 80. A second opening 82 isprovided in the small truncated end of tube 76 which, likewise, is sizedsmaller than ball 80. Opening 82 defines a controlled orifice open tothe atmosphere into which air is aspirated at a velocity sufficient tolift ball 80 depending upon the magnitude of the negative pressuregradient thereacross. The outside of tube 76 is provided withscale-forming indicia 84 reading directly in negative pressure measuredin cm H₂ O or some other suitable set of values.

Now, while floating ball-type indicators of the same general type asthat just described have been used for many years to indicate flow ratesin a flowing fluid, to applicant's knowledge no such indicator has beenused heretofore to read negative pressures existent in the air chamberof a chest drainage system. When so used, the attending physician andothers responsible for the safety and well being of the patient areprovided with an easily readable pressure gauge constantly monitoringthe negative pressure within chambr 20. Having thus described thefail-safe system that becomes functional whenever a positive pressureabove a predetermined level is present in air chamber 20, a similarsystem will next be set forth which responds in like manner to handleabnormal negative pressures within the system for which purpose detailedreference will be made to FIG. 3.

Excess negative pressure are rare but could, conceivably, result from aso-called "milking" or stripping of chest drainage tube 66. If thisshould occur or if for some reason an abnormal negative pressure ispresent in air chamber 20, such a condition will immediately exist inthe fluid collection chambers 26 as well. If the negative pressurecondition occurs upstream of the system, the fluid in U-tube 62 would besucked out into the discharge tube and ultimately back into thepatient's chest cavity if it were not for the presence of negativepressure relief valve 60. Likewise, if a sudden high negative pressurewere to occur in air chamber 20 for some reason, relief valve 16 will beclosed and check valve 14 will be open exposing the fluid collectionchambers 26 and everything upstream thereof including the patient tothis abnormal condition. With the instant system, relief valve 60connected into the fluid free air space 86 above the fluid containedwithin the fluid collection chambers 26 will respond by opening asillustrated to admit air from the atmosphere thus limiting the maximumnegative pressure that can exist in the system to a predetermined levelwell below that where any backflow to the patient can take place.Negative pressure relief valve 60 is of the more or less commonpoppet-type except that it incorporates bacterial filter 88 (FIG. 3)which filters the incoming air to prevent contamination of the fluidsstored in the fluid collection chambers. Valve 60 is detachablyconnected to neck 90 of the bottle by means of a short length of hose 92in the particular form shown. The particular system illustrated hasvalve 60 set to open at a maximum negative pressure of -50 cm H₂ O whichhas proven entirely adequate to protect the patient. Once again, theaccuracy necessary for precise controlled operation of the system isfound in valve 60 and is not demanded of throw away bottle 10 whichmerely provides a connection 90 open to the atmosphere upon which toattach same. FIG. 3 illustrates diagrammatically the condition describedabove where an excessive negative pressure is sensed in air chamber 20that causes the valve element 94 of valve 60 to move off its aperturedseat 96 in opposition to the bias of spring 98 and thus open to maintainthe system pressure at a maximum of -50 cm H₂ O.

In closing, reference will be made to FIG. 5 wherein a unique capabilityof the instant bottle 10 has been illustrated, namely, the use thereofin inverted position as a reservoir to return the previously drainedchest fluids back into the patient's chest cavity. Without having totransfer these fluids or otherwise handle them with the attendant riskof contamination, drainage hose 66 is clamped off by clamp 100,subassembly 12 removed and a fluid delivery tube 102 fitted in its placeto air outlet 42. Valve 60 need not be removed since it will remain inits normally-closed condition. After tube 102 has been inserted into thepatient's chest cavity, the bottle can be inverted to dispense thefluids stored therein by gravity flow. No other chest drainage system toapplicant's knowledge has a bottle that can be used in this way.

What is claimed is:
 1. A non-waterseal thoracic drainage apparatuscomprising:means defining a fluid collection chamber having an air spaceat its upper end; an inlet tube in communication with the fluidcollection chamber, the inlet tube being connectable to receive fluidsand air from a patient's a chest cavity. one-way waterless valve meansassociated with the fluid collection chamber and being operative,unaided by underwater seals, to permit air to flow out of the air spacewhile preventing reverse flow back into the collection chamber; meansdefining a flow path between the inlet tube and said one-way waterlessvalve means; air leak indicator means along said flow path forentrapping a volume of liquid through which air may bubble; said airleak indicator means being constructed to provide a visual indication ofair passing therethrough; and said one-way waterless valve means beingopenable in response to a low pressure differential.
 2. A thoracicdrainage apparatus as defined in claim 1 wherein said entrapping meanscomprises a portion of the flow path being U-shaped.
 3. A thoracicdrainage apparatus as defined in claim 2 further comprising:an outletport in communication with the air space, the outlet port being adaptedto be connected to a source of suction.
 4. A thoracic drainage apparatusas defined in claim 3 further comprising:suction control means forcontrolling the level of suction applied to the air space.
 5. A thoracicdrainage apparatus as defined in any of claims 1-4 furthercomprising:means defining a high negative pressure relief valve incommunication with the air space, said relief valve being operative toopen whenever the negative pressure in the air space exceeds apredetermined value, the high negative pressure relief valve means beingin communication with a source of increased pressure to admit air to theair space when said high negative pressure relief valve means opens. 6.A thoracic drainage apparatus as defined in any of claims 1-5 furthercomprising:positive pressure relief valve means in communication withthe air space.
 7. A non-waterseal thoracic drainage apparatuscomprising:means defining a fluid collection chamber having an air spaceat its upper end; an inlet tube in communication with the fluidcollection chamber, the inlet tube being connectable to receive fluidsand air from a patient a chest cavity; one-way waterless valve meansassociated with the fluid collection chamber and being operative,unaided by underwater seals, to permit air to flow out of the air spacewhile preventing reverse flow back into the collection chamber, saidone-way waterless valve means comprising the primary means forpreventing said reverse flow; means defining a flow path between theinlet tube and said one-way waterless valve means; air leak indicatormeans along said flow path for entrapping a volume of liquid throughwhich air may bubble; and said air leak indicator means beingconstructed to provide a visual indication of air passing therethrough8. A thoracic drainage apparatus as defined in claim 7 wherein saidentrapping means comprises a portion of the flow path being U-shaped. 9.A thoracic drainage apparatus as defined in claim 8 furthercomprising:an outlet port in communication with the air space, theoutlet port being adapted to be connected to a source of suction.
 10. Athoracic drainage apparatus as defined in claim 9 furthercomprising:suction control means for controlling the level of suctionapplied to the air space.
 11. A thoracic drainage apparatus as definedin any of claims 7-10 further comprising:means defining a high negativepressure relief valve in communication with the air space, said reliefvalve being operative to open whenever the negative pressure in the airspace exceeds a predetermined value, the high negative pressure reliefvalve means being in communication with a source of increased pressureto admit air to the air space when said high negative pressure reliefvalve means opens.
 12. A thoracic drainage apparatus as defined in anyof claims 7-11 further comprising:positive pressure relief valve meansin communication with the air space.
 13. A thoracic drainage apparatusas defined in claim 12 further comprising:said one-way valve having anoutlet side which communicates with the outlet port; the positivepressure relief valve having an outlet side which does not communicatewith the outlet port thereby to define separate outlet paths for theone-way valve and positive pressure relief means.
 14. A thoracicdrainage apparatus as defined in any of claims 7-13 wherein the one-waywaterless valve means is openable in response to a low pressuredifferential.
 15. A thoracic drainage apparatus as defined in claim 14wherein said low pressure differential is approximately 0.5 cm water.